The present invention relates to a method of manufacturing composite articles in general, and more particularly to such a method as employed in manufacturing articles from a non-flowable mixture, and also to articles obtained by resorting to this method.
There has been already proposed a method of manufacturing composite articles, particularly such which are provided, at least at a predetermined region of the exposed surface thereof, with a decorative coating layer, in which a non-flowable mixture of fibrous material admixed with a heat-hardening binder is pressed in such a manner that, first of all, a preform in made from the mixture by cold pressing, the preform is introduced together with the decorative coating layer or coating layers in a hot press where the mixture which has been previously pressed into the preform hardens during the hot pressing operation performed in the hot press, and simultaneously, the preform is bonded with the decorative coating layer or layers at the above-mentioned region or, when desired all over the exposed surface thereof.
This method is already known and in widespread use, and the materials used and the temperature and pressure conditions to which such materials are subjected are well known and available to those active in this field. Such a method is used for the manufacture of a variety of different profiled composite articles, such as facing elements used in the building industry, for instance, cladding panels, plates or profiled elements used for either internal or external cladding of walls or the like, balcony cladding elements, window sills, table tops and the like.
The non-flowable mixture, most of the time, consists of lignocellulose-containing fibrous materials, such as comminuted and dried wood chips, bagasse fibers and the like, which are admixed with a heat-hardening synthetic plastic resin, such as a melamine resin, urea formaldehyde resin or phenol formaldehyde resin. Instead of the comminuted and dried wood or bagasse fibers, there can also be used fibers of other materials, such as glass fibers steel wool or asbestos fibers, either individually or in a mixture with one another, to which corresponding, preferably organic, binders are added.
The coating layer mostly consists of at least two sub-layers, that is a decorative layer, for example, of a fabric, a veneer, a printed paper sheet or foil or a synthetic plastic material foil, over which there can be applied a transparent protective layer. As the protective layer, there is usually used a clear so-called overlay paper, consisting of a non-filled alpha-cellulose paper or a glass fiber fleece, which is soaked with a thermosetting plastic material, mostly on the melamine basis. The transparent protective layer can also be produced in such a manner that the decorative layer is provided with a thicker resin layer, such as of melamine formaldehyde resin or urea formaldehyde resin.
It will be appreciated that it is desirable and, most of the time, even indispensible, that the coating layer enters into a permanent bond with the exposed surface of the preform in order to, whenever necessary, assure a weather and moisture resistant encapsulation of the profiled body. For the latter reason, and not only for aesthetical reasons, it is necessary that the coating layer be provided over the entire exposed surface of the preform, that is, not only on the major surfaces of the preform, but also on the edges and on the edge zones which enclose an obtuse angle with the major surfaces of the preform. It is also desired, under these conditions, that the coating layer be smooth and flat at such zones.
As already mentioned before, the above-discussed conventional methods of manufacturing composite articles have been proven to be effective, particularly in a series production, for manufacturing composite articles of various shapes. Nevertheless, it could be observed, time and time again, on the finished composite articles, that the coating layer was not absolutely smooth and flat, particularly at the edge zones, but rather contained waves or folds at such zones. This, of course, is rather disadvantageous, particularly where the preform is to be transformed into the final article in such a manner that the entire body obtained from the preform is encapsulated in the coating layer.